The Peebles-based businessman has confirmed he is behind a rival offer for UBIG's 50% shareholding, which the Foundation hope to get for nothing after Friday's Company Voluntary Arrangement was agreed.
Persuading UBIG to part with their stake remains the only major hurdle for the club's administrators BDO after secured creditor Ukio Bankas accepted £2.5m for debts of £15.5m their 29.9% stake. But now collapsed Lithuanian investment company UBIG, who are owed £8.2m, must consider Jamieson's offer.
Jamieson went up against the Foundation, who have nearly 8000 fans making monthly pledges, in his failed attempt to gain preferred bidder status and is still refusing to back down. Hearts administrator Bryan Jackson said at the weekend that such actions could derail his bid to lead the club out of administration and the Foundation have criticised his disruptive behaviour.
A spokesperson for the Foundation said: "We note the comments from BDO's Bryan Jackson and share his concern. This is a very complicated and delicate situation and would urge any third party who is attempting to place an unfunded and fanciful rival bid to reflect on the potential damage this could do to the CVA process. This is too important to the future of Heart of Midlothian to have a Walter Mitty character destabilise the progress of getting the club out of administration because of a desire for publicity or attention."
Amid a complex administration process, it is thought that Jamieson - should his bid be successful - would effectively be left with a 50% stake in a club which would be liquidated. The Foundation's offer is subject to being handed UBIG's shareholding.
Responding to the Foundation's claim that his bid was fanciful and he was a Walter Mitty character, Jamieson said yesterday: "That's their decision to come out with that, that's nonsense. It's not fanciful, I can assure you."